It is known in the art to include an air gap (i.e., a cavity filled with a gas having a low dielectric constant) in a bipolar transistor structure to provide isolation supporting a reduction in base-collector capacitance. See, for example, Unites States Patent Application Publication No. 2010/0187657. The process flow for fabrication of such a transistor in accordance with the prior art is quite complex and includes provision of a dielectric multilayer and multiple dry and wet etching operations. There are also concerns with connection to the intrinsic base as well as the fabrication of an intrinsic collector by epitaxy.
There exists a need in the art to provide a better fabrication process for the realization of air gap isolation structures. The also exists a need in the art to provide a better bipolar transistor collector/base isolation for improving transistor performance.